/Engine/Source/Runtime/Slate/Public/Framework/Docking/LayoutExtender.h
Extend the tab stack identified by the specified extension ID
void ExtendStack ( [FName](API\Runtime\Core\UObject\FName) ExtensionId, ELayoutExtensionPosition Position, [FTabManager::FTab](API\Runtime\Slate\Framework\Docking\FTabManager\FTab) TabToAdd )